Linux Advanced

chbin · 03-17-2005, 01:58 AM

Short of using a ramdisk or writting C code, is there a way for me to put a 30 MB file into memory. I want to run a grep search on a 30 MB file every 15 minutes or so. It would be way more efficient if I could just manually chuck it into memory and run grep on it there and then just leave it there until I want to grep it again. Is there some directory, /sys, or /dev think I could use to accomplish this?

keefaz · 03-17-2005, 05:24 AM

I would think grep never loads the whole file in memory, instead it loads line by line
Quote me and explain if I am wrong

eddie0uk · 03-17-2005, 05:52 AM

What about /dev/shm?

tmpfs 1584M 0 1584M 0.0 [ ] /dev/shm

gbonvehi · 03-17-2005, 07:41 AM

Try (you can change /mnt/ramdisk, be sure that the dir exists):

Code:

mount -t ramfs ramfs /mnt/ramdisk

then copy the file into it, and grep it there (it's on memory now until you umount or remove it

Another approach is to use a tmpfs as eddie0uk said, but I've never used it before.

Update: I've just tried, it's the same but you can also specify a size for it, ie:

Code:

mount -t tmpfs -o size=30M tmpfs /mnt/ramdisk

chbin · 03-17-2005, 11:53 AM

cool, thanks. I like the tmpfs better.

chbin · 03-17-2005, 12:00 PM

I just tried it and it works great. Man linux is so cool.

sh1ft · 03-17-2005, 01:16 PM

Try doing that on windows

perfect_circle · 03-17-2005, 01:41 PM

Quote:

Originally posted by sh1ft
Try doing that on windows

I had the same impression. That you couldn't do that in windows but there are programs (most of them commercial of course...) for that.
http://www.winsoft.sk/ramdisk.htm
http://users.compaqnet.be/cn181612/R...amdiskfree.htm
http://www.ei-europe.com/ramdisk.html
I think microsoft has a ramdisk sys driver...

chbin · 03-17-2005, 01:59 PM

Yeah you can do it in windows with a ramdisk but you have to pay for the ramdisk software. Then reboot and tell it the size and then you lose that memory permanetly until you reboot, which sucks.

With the tmpfs, you can do it on the fly and then remove it and continue as if nothing had happened.

chbin · 03-17-2005, 03:28 PM

Doesn't tmpfs my ramdisk obsolete. Now I'm thinking why does pat use an initrd image and then mount into with a ramdisk? Because the memory allocated to the ramdisk can never be gottin back. With tmpfs it can grow and shrink or just disappear depending on you.

chbin · 03-17-2005, 03:47 PM

Wow, tmpfs is so cool. I was thinking maybe I can mount my /tmp directory and a few others that have a lot of disk I/O into tmpfs. Any recommendation on stuff that are good candidates?

DaWallace · 03-17-2005, 05:07 PM

Quote:

Originally posted by chbin
Doesn't tmpfs my ramdisk obsolete. Now I'm thinking why does pat use an initrd image and then mount into with a ramdisk? Because the memory allocated to the ramdisk can never be gottin back. With tmpfs it can grow and shrink or just disappear depending on you.

pat has been reluctant to do even that, it wasn't in older versions.. also I'm not sure how and if that would work.